A measuring system for measuring the Internet Protocol (IP) performance parameters, such as one-way delay, IP delay variations, and packet losses, in IP networks is known from non-prepublished German Patent Application DE 100 46 240.5. The subject matter of non-prepublished German Patent Application DE 101 28 927.8 is a method that allows time stamps to be generated in the measuring system even when access to a reference clock is blocked for a short time.
The measuring system underlying these patent applications is a distributed measuring system, i.e., the individual components of the measuring system are spatially distributed and interconnected via a telecommunications network. This measuring system includes at least two measuring computers, a database in which the measurement results and the configuration of the measuring system are stored, a control computer controlling the measuring computers for determining the measurement result, as well as various graphical user interfaces, in particular for configuring the measuring system and visualizing the obtained measurement results.
In order to carry out the measuring method, a unidirectional measurement path is established between at least two measuring computers. On this measurement path, measurement packets are sent from a first measuring computer to a second measuring computer with a configurable distribution in time.
In the process, the departure of the measurement packet from the first measuring computer is recorded; i.e., a first time stamp is generated. This first time stamp is transmitted to the second measuring computer together with the measurement packet and other data, such as sequence numbers. The second measuring computer records the arrival of the measurement packet and generates a second time stamp.
To allow the one-way delay resulting from the difference of the two time stamps to be determined with sufficient accuracy, the time stamps generated by the measuring computers need to be synchronized with sufficient accuracy. To this end, the time stamps may be generated using a satellite system, such as GPS (Global Positioning System), acting as a time source, or from local clocks that are synchronized via NTP (Network Time Protocol).
The measurement results are retrieved by the control computer from the second measuring computer as measured data and stored in a database, where they are made available for visualization. The measured data and the system status may optionally be displayed via an offline display or an online display. In this context, “offline display” means that the display of the measured data must be initiated manually via a browser while in the case of the online display, the display is automatically updated and displayed at a certain time interval. The above-mentioned graphical user interfaces are used for this purpose.
The configuration of the measuring system is also carried out using the aforementioned graphical user interface. To this end, the user enters information about the type and course of the measurement. The information entered is stored in the database; the control computer reads out this configuration data, configures the measuring computers accordingly, and starts or stops the measurement connections according to this data.